Flashtube



June 14, 1960 Fig}.

E. NoLLE FLASHTUBE Filed Dec. 28, 1956 lnven tov: firns t NciLLe His A ttow-neg.

United States Patent FLASHTUBE Ernst Niille, Berlin-Charlottenburg,Germany, assignor to Patent-Treuhand-Gesellschaft fiir ElektrischeGliihlampen m.b.H. (Patent Fiduciary Company for Electric IncandescentLamps Ltd.), a German company Filed Dec. 28, 1956, Ser. No. 631,179

Claims priority, application Germany Jan. 27, 1956 2 Claims. (Cl.313-185) This invention relates to an electric discharge lamp of theflashtube type for pulse or stroboscopic applications, the cathode ofwhich consists of or contains a sintered porous body for the purpose ofobtain ng a rapid discharge and assuring long life.

For the operation of flashtubes at higher flashing frequencies orrepetition rates, rapid development of the arc discharge is required aswell as quick extinction and tie-ionization. It has already beenproposed to use as a cathode for a flashtube a non-homogeneous andporous body of sintered metallic powder whereby the transition from thefirst starting glow discharge into the are discharge is facilitated anda decrease of the extinguishing voltage is obtained.

The object of the invention is to provide a flashtube having an improvedcathode construction which achieves more rapid development andsubsequent extinction of the arc discharge.

According to the invention, a flash tube or electric discharge lamp forpulse operation is provided with a cathode body consisting of sinterednickel powder provided with cavities such as borings, recesses orgrooves. These cavities act as hollow cathodes and assure that an arcdischarge takes place shortly after the glow discharge has started; inother words, they assure rapid build-up of the discharge. The cavitiesalso augment the cathode surface available and thereby increase the lifeof the cathode and consequently of the lamp. It has proved advantageousto make the grooves about 0.5 mm. deep and to choose a diameter of about0.5 mm. for the borings. Suitably the cathode is activated with caesiumchloride which is highly advantageous in a lamp intended forstroboscopic applications because of the self-extinguishing efiectobtained thereby. Flashtubes With such cathodes are suitably providedwith a neon filling at a pressure in the range of 10 to 40 millimetersof mercury.

The accompanying drawing shows an example of a cathode for a flashtubeaccording to the present invention wherein:

Fig. 1 is a side view of the cathode end of a flashtube shown partly insection.

Fig. 2 is a plan view of same, that is a view looking along the axis ofthe tube.

Referring to the drawing, a metal cup 1 contains a cathode body 2consisting of sintered nickel powder; a current inlead 3 is attached asby welding to the cup and serves also as a support. The cathode body 2is provided with axial borings 4, the diameter of which is about 0.5millimeter. The borings open into the front face oi the body on whichthe discharge terminates, and, as illustrated in Fig. 2, they may befive in number. The cathode body is also provided on its circumferencewith numerous axial grooves 5 which are about 0.5 millimeter deep in atransverse or radial direction. The active surface of the cathode isincreased by the cavities consisting of the borings and grooves, wherebya rapid ice change from glow to are discharge is achieved and a longlength of life is realized for the flash tube.

The sintered cathode body is activated with caesium chloride, forinstance by immersion in a saturated solution thereof in distilled waterfollowed by drying. It has been found that activation with caesiumchloride reduces the time required for extinction and de-ionization inthe flashtube after a discharge or flash; thus a higher repetition rateof flashing may be achieved.

The instant cathode is mounted in a slender elongated vitreous tube 6 ofwhich one end is illustrated in the drawing, the current inlead 3 beingsealed or pressed into the flattened or pressed tube end 7. The tube maybe of straight linear form or curved into a U-shape or helix in knownmanner. In the preferred embodiment of a flashtube illustrated in thedrawing, the metal cup 1 is large relative to the internal diameter ofthe vitreous tube 6 and has a diameter not less than approximately halfthe internal diameter of the tube. The other end of the tube may beprovided with an anode which may, if desired, be merely the end of aninlead. The tube is filled with an ionizable medium such as an inert gasat a low pressure. A suitable filling consists of neon at a pressure ofin the range of 10 to 40 millimeters of mercury, preferably at about 15millimeters of mercury.

While a certain specific embodiment of the invention has beenillustrated and described in detail, the same is intended as anillustrative example only, and the scope of the invention is to bedetermined by the appended claims.

What is claimed as new and desired to be secured by Letters Patent ofthe United States is:

1. An electric flashtube comprising a slender elongated vitreousenvelope having sealed into opposite ends thereof a cathode and ananode, said cathode comprising an open-ended metal cup having a diameternot less than approximately half the internal diameter of said envelopeand containing a porous body of sintered nickel powder provided withcavities achieving a hollow cathode effect for rapid build-up of a flashdischarge and activated with caesium chloride to assure rapidextinguishment and de-ionization subsequent to said discharge, saidcavities having a transverse dimension of approximately 0.5 millimeterand a filling within said envelope of an inert gas at a pressure in therange of 10 to 40 millimeters of mercury.

2. An electric flashtube comprising a slender elongated vitreousenvelope having sealed into opposite ends thereof a cathode and ananode, said cathode comprising an open-ended metal cup having a diameternot less than approximately half the internal diameter of said envelopeand containing a porous body of sintered nickel powder provided withcavities achieving a hollow cathode effect for rapid build-up of a flashdischarge and activated with caesium chloride to assure rapidextinguishment and deionization subsequent to said discharge, saidcavities having a transverse dimension of approximately 0.5 millimeterand a filling within said envelope of neon at a pressure ofapproximately 15 millimeters of mercury.

References Cited in the file of this patent UNITED STATES PATENTS1,552,310 Kayko Sept. 1, 1925 1,716,545 Mackay June 11, 1929 2,107,945Hull Feb. 8, 1938 2,147,447 Kolligs Feb. 14, 1939 2,159,747 MendenhallMay 23, 1939 2,180,988 Lemmers Nov. 21, 1939

